Minimum time control for multiphase buck converter: analysis and application

The combination of minimum time control and multiphase converter is a favorable option for dc-dc converters in applications where output voltage variation is required, such as RF amplifiers and dynamic voltage scaling in microprocessors, due to their advantage of fast dynamic response. In this paper, an improved minimum time control approach for multiphase buck converter that is based on charge balance technique, aiming at fast output voltage transition is presented. Compared with the traditional method, the proposed control takes into account the phase delay and current ripple in each phase. Therefore, by investigating the behavior of multiphase converter during voltage transition, it resolves the problem of current unbalance after the transient, which can lead to long settling time of the output voltage. The restriction of this control is that the output voltage that the converter can provide is related to the number of the phases, because only the duty cycles at which the multiphase converter has total ripple cancellation are used in this approach. The model of the proposed control is introduced, and the design constraints of the buck converters filter for this control are discussed. In order to prove the concept, a four-phase buck converter is implemented and the experimental results that validate the proposed control method are presented. The application of this control to RF envelope tracking is also presented in this paper.

Quantity of CO2 Emissions in the Life Cycle of a Highway Infrastructure.

The complexity of climate change and its evolution during the last few years has a positive impact on new developments and approaches to reduce the emissions of CO2. Looking for a methodology to evaluate the sustainability of a roadway, a tool has been developed. Life Cycle Assessment (LCA) is being accepted by the road industry to measure and evaluate the environmental impacts of an infrastructure, as the energy consumption and carbon footprint. This paper describes the methodology to calculate the CO2 emissions associated with the energy embodied on a roadway along its life cycle, including construction, operations and demolition. It will assist to find solutions to improve the energy footprint and reduce the amount of CO2 emissions. Details are provided of both, the methodology and the data acquisition. This paper is an application of the methodology to the Spanish highways, using a local database. Two case studies and a practical example are studied to show the model as a decision support for sustainable construction in the road industry.

Planar point sets with large minimum convex decompositions

We show the existence of sets with n points (n ? 4) for which every convex decomposition contains more than (35/32)n?(3/2) polygons,which refutes the conjecture that for every set of n points there is a convex decomposition with at most n+C polygons. For sets having exactly three extreme pointswe show that more than n+sqr(2(n ? 3))?4 polygons may be necessary to form a convex decomposition.

Simulación de seguimiento de blancos en sistemas radar. Parte 2

El proyecto consiste en el diseño y estudio de un software cuyas prestaciones estén orientadas a gestionar una simulación de un sistema de radar. El prototipo de este entorno de simulación se ha realizado en el lenguaje Matlab debido a que inicialmente se considera el más adecuado para el tratamiento de las señales que los sistemas de radar manejan para realizar sus cálculos. Se ha escogido como modelo el software desarrollado por la compañía SAP para gestionar los E.R.P.s de grandes empresas. El motivo es que es un software cuyo diseño y funcionalidad es especialmente adecuado para la gestión ordenada de una cantidad grande de datos diversos de forma integrada. Diseñar e implementar el propio entorno es una tarea de enorme complejidad y que requerirá el esfuerzo de una cantidad importante de personas; por lo que este proyecto se ha limitado, a un prototipo básico con una serie de características mínimas; así como a indicar y dejar preparado el camino por el que deberán transcurrir las futuras agregaciones de funcionalidad o mejoras. Funcionalmente, esto es, independientemente de la implementación específica con la que se construya el entorno de simulación, se ha considerado dividir las características y prestaciones ofrecidas por el sistema en bloques. Estos bloques agruparán los componentes relacionados con un aspecto específico de la simulación, por ejemplo, el bloque 1, es el asignado a todo lo relacionado con el blanco a detectar. El usuario del entorno de simulación interactuará con el sistema ejecutando lo que se llaman transacciones, que son agrupaciones lógicas de datos a introducir/consultar en el sistema relacionados y que se pueden ejecutar de forma independiente. Un ejemplo de transacción es la que permite mantener una trayectoria de un blanco junto con sus parámetros, pero también puede ser una transacción la aplicación que permite por ejemplo, gestionar los usuarios con acceso al entorno. Es decir, las transacciones son el componente mínimo a partir del cual el usuario puede interactuar con el sistema. La interfaz gráfica que se le ofrecerá al usuario, está basada en modos, que se pueden considerar “ventanas” independientes entre sí dentro de las cuáles el usuario ejecuta sus transacciones. El usuario podrá trabajar con cuantos modos en paralelo desee y cambiar según desee entre ellos. La programación del software se ha realizado utilizando la metodología de orientación a objetos y se ha intentado maximizar la reutilización del código así como la configurabilidad de su funcionalidad. Una característica importante que se ha incorporado para garantizar la integridad de los datos es un diccionario sintáctico. Para permitir la persistencia de los datos entre sesiones del usuario se ha implementado una base de datos virtual (que se prevé se reemplace por una real), que permite manejar, tablas, campos clave, etc. con el fin de guardar todos los datos del entorno, tanto los de configuración que solo serían responsabilidad de los administradores/desarrolladores como los datos maestros y transaccionales que serían gestionados por los usuarios finales del entorno de simulación. ABSTRACT. This end-of-degree project comprises the design, study and implementation of a software based application able to simulate the various aspects and performance of a radar system. A blueprint for this application has been constructed upon the Matlab programming language. This is due to the fact that initially it was thought to be the one most suitable to the complex signals radar systems usually process; but it has proven to be less than adequate for all the other core processes the simulation environment must provide users with. The software’s design has been based on another existing software which is the one developed by the SAP company for managing enterprises, a software categorized (and considered the paradigm of) as E.R.P. software (E.R.P. stands for Enterprise Resource Planning). This software has been selected as a model because is very well suited (its basic features) for working in an orderly fashion with a pretty good quantity of data of very diverse characteristics, and for doing it in a way which protects the integrity of the data. To design and construct the simulation environment with all its potential features is a pretty hard task and requires a great amount of effort and work to be dedicated to its accomplishment. Due to this, the scope of this end-of-degree project has been focused to design and construct a very basic prototype with minimal features, but which way future developments and upgrades to the systems features should go has also been pointed. In a purely functional approach, i.e. disregarding completely the specific implementation which accomplishes the simulation features, the different parts or aspects of the simulation system have been divided and classified into blocks. The blocks will gather together and comprise the various components related with a specific aspect of the simulation landscape, for example, block number one will be the one dealing with all the features related to the radars system target. The user interaction with the system will be based on the execution of so called transactions, which essentially consist on bunches of information which logically belong together and can thus be managed together. A good example, could be a transaction which permits to maintain a series of specifications for target’s paths; but it could also be something completely unrelated with the radar system itself as for example, the management of the users who can access the system. Transactions will be thus the minimum unit of interaction of users with the system. The graphic interface provided to the user will be mode based, which can be considered something akin to a set of independent windows which are able on their own to sustain the execution of an independent transaction. The user ideally should be able to work with as many modes simultaneously as he wants to, switching his focus between them at will. The approach to the software construction has been based on the object based paradigm. An effort has been made to maximize the code’s reutilization and also in maximizing its customizing, i.e., same sets of code able to perform different tasks based on configuration data. An important feature incorporated to the software has been a data dictionary (a syntactic one) which helps guarantee data integrity. Another important feature that allow to maintain data persistency between user sessions, is a virtual relational data base (which should in future times become a real data base) which allows to store data in tables. The data store in this tables comprises both the system’s configuration data (which administrators and developers will maintain) and also master and transactional data whose maintenance will be the end users task.

Critical radius for hot-jet ignition of hydrogen-air mixtures

This study addresses deflagration initiation of lean and stoichiometric hydrogen–air mixtures by the sudden discharge of a hot jet of their adiabatic combustion products. The objective is to compute the minimum jet radius required for ignition, a relevant quantity of interest for safety and technological applications. For sufficiently small discharge velocities, the numerical solution of the problem requires integration of the axisymmetric Navier–Stokes equations for chemically reacting ideal-gas mixtures, supplemented by standard descriptions of the molecular transport terms and a suitably reduced chemical-kinetic mechanism for the chemistry description. The computations provide the variation of the critical radius for hot-jet ignition with both the jet velocity and the equivalence ratio of the mixture, giving values that vary between a few tens microns to a few hundred microns in the range of conditions explored. For a given equivalence ratio, the critical radius is found to increase with increasing injection velocities, although the increase is only moderately large. On the other hand, for a given injection velocity, the smallest critical radius is found at stoichiometric conditions.

Consideration of tip speed limitations in preliminary analysis of minimum COE wind turbines

A relation between Cost Of Energy, COE, maximum allowed tip speed, and rated wind speed, is obtained for wind turbines with a given goal rated power. The wind regime is characterised by the corresponding parameters of the probability density function of wind speed. The non-dimensional characteristics of the rotor: number of blades, the blade radial distributions of local solidity, twist angle, and airfoil type, play the role of parameters in the mentioned relation. The COE is estimated using a cost model commonly used by the designers. This cost model requires basic design data such as the rotor radius and the ratio between the hub height and the rotor radius. Certain design options, DO, related to the technology of the power plant, tower and blades are also required as inputs. The function obtained for the COE can be explored to �nd those values of rotor radius that give rise to minimum cost of energy for a given wind regime as the tip speed limitation changes. The analysis reveals that iso-COE lines evolve parallel to iso-radius lines for large values of limit tip speed but that this is not the case for small values of the tip speed limits. It is concluded that, as the tip speed limit decreases, the optimum decision for keeping minimum COE values can be: a) reducing the rotor radius for places with high weibull scale parameter or b) increasing the rotor radius for places with low weibull scale parameter

Strategies for Minimum Distance in Simulated Evacuation of Transport Airplanes

The present paper describes the preliminary stages of the development of a new, comprehensive model conceived to simulate the evacuation of transport airplanes in certification studies. Two previous steps were devoted to implementing an efficient procedure to define the whole geometry of the cabin, and setting up an algorithm for assigning seats to available exits. Now, to clarify the role of the cabin arrangement in the evacuation process, the paper addresses the influence of several restrictions on the seat-to-exit assignment algorithm, maintaining a purely geometrical approach for consistency. Four situations are considered: first, an assignment method without limitations to search the minimum for the total distance run by all passengers along their escaping paths; second, a protocol that restricts the number of evacuees through each exit according to updated FAR 25 capacity; third, a procedure which tends to the best proportional sharing among exits but obliges to each passenger to egress through the nearest fore or rear exits; and fourth, a scenario which includes both restrictions. The four assignment strategies are applied to turboprops, and narrow body and wide body jets. Seat to exit distance and number of evacuees per exit are the main output variables. The results show the influence of airplane size and the impact of non-symmetries and inappropriate matching between size and longitudinal location of exits.

Evolutionary computation of forests with Degree- and Role-Constrained Minimum Spanning Trees

Finding the degree-constrained minimum spanning tree (DCMST) of a graph is a widely studied NP-hard problem. One of its most important applications is network design. Here we deal with a new variant of the DCMST problem, which consists of finding not only the degree- but also the role-constrained minimum spanning tree (DRCMST), i.e., we add constraints to restrict the role of the nodes in the tree to root, intermediate or leaf node. Furthermore, we do not limit the number of root nodes to one, thereby, generally, building a forest of DRCMSTs. The modeling of network design problems can benefit from the possibility of generating more than one tree and determining the role of the nodes in the network. We propose a novel permutation-based representation to encode these forests. In this new representation, one permutation simultaneously encodes all the trees to be built. We simulate a wide variety of DRCMST problems which we optimize using eight different evolutionary computation algorithms encoding individuals of the population using the proposed representation. The algorithms we use are: estimation of distribution algorithm, generational genetic algorithm, steady-state genetic algorithm, covariance matrix adaptation evolution strategy, differential evolution, elitist evolution strategy, non-elitist evolution strategy and particle swarm optimization. The best results are for the estimation of distribution algorithms and both types of genetic algorithms, although the genetic algorithms are significantly faster.

Minimum volume stability limits for axisymmetric liquid bridges subject to steady axial acceleration

In this paper the influence of an axial microgravity on the minimum volume stability limit of axisymmetric liquid bridges between unequal disks is analyzed both theoretically and experimentally. The results here presented extend the knowledge of the static behaviour of liquid bridges to fluid configurations different from those studied up to now (almost equal disks). Experimental results, obtained by simulating microgravity conditions by the neutral buoyancy technique, are also presented and are shown to be in complete agreement with theoretical ones.

Stability limits of minimum volume and breaking axisymmetric liquid bridges between unequal disks

This paper deals with the stability limits of minimum volume and the breaking of axisymmetric liquid columns held by capillary forces between two concentric,circular solid disk of different radii. The problem has been analyzed both theoreti-cally and experimentally. A theoretical analysis concerning the breaking of liquid bridges has been performed by using a one-dimensional slice model already used in liquid bridge problems. Experiments have been carried out by using milli-metric liquid bridges, and minimum volume stability limits as well as the volumes of the drops resulting after breaking have been measured for a large number of liquid bridge configurations. Experimental results being in agreement with theoretical prediction.

An experimental study of the breakage of liquid bridges at stability limit of minimum volume

An experimental apparatus to study the breaking process of axisymmetric liquid bridges has been developed, and the breaking sequences of a large number of liquid bridge configurations at minimum-volume stability limit have been analyzed. Experimental results show that very close to the breaking moment the neck radius of the liquid bridge varies as t1/3, where t is the time to breakage, irrespective of the value of the distance between the solid disks that support the liquid column.

A group decision-making methodology with incomplete individual beliefs applied to e-Democracy

We consider the situation where there are several alternatives for investing a quantity of money to achieve a set of objectives. The choice of which alternative to apply depends on how citizens and political representatives perceive that such objectives should be achieved. All citizens with the right to vote can express their preferences in the decision-making process. These preferences may be incomplete. Political representatives represent the citizens who have not taken part in the decision-making process. The weight corresponding to political representatives depends on the number of citizens that have intervened in the decision-making process. The methodology we propose needs the participants to specify for each alternative how they rate the different attributes and the relative importance of attributes. On the basis of this information an expected utility interval is output for each alternative. To do this, an evidential reasoning approach is applied. This approach improves the insightfulness and rationality of the decision-making process using a belief decision matrix for problem modeling and the Dempster?Shafer theory of evidence for attribute aggregation. Finally, we propose using the distances of each expected utility interval from the maximum and the minimum utilities to rank the alternative set. The basic idea is that an alternative is ranked first if its distance to the maximum utility is the smallest, and its distance to the minimum utility is the greatest. If only one of these conditions is satisfied, a distance ratio is then used.

Some aspects of lubrication in heavy regimes: thermal effects, stability and turbulence

In this work, a combination of numerical methods applied to thermohydrodynamic lubrication problems with cavitation is presented. It should be emphasized the difficulty of the nonlinear mathematical coupled model involving a free boundary problem, but also the simplicity of the algorithms employed to solve it. So, finite element discretizations for the hydrodynamic and thermal equations combined with upwind techniques for the convection terms and duality methods for nonlinear features are proposed. Additionally, a model describing the movement of the shaft is provided. Considering the shaft as a rigid body this model will consist of an ODE system relating acceleration of the center of gravity and external and pressure loads. The numerical experiments of mechanical stability try to clarify the position of the neutral stability curve. Finally, a rotating machine for ship propulsion involving both axial and radial bearings operating with nonconventional lubricants (seawater to avoid environmental pollution) is analyzed by using laminar and turbulent inertial flows.

Proposal of a new indicator to define ductility applied to corroded steel reinforcement on concrete structures = Propuesta de un nuevo indicador para definir la ductilidad aplicada a la corrosión del acero de refuerzo en estructuras de hormigón

The carbonation of concrete or the chlorides ingress in such quantity to reach the level of bars is triggers of reinforcement corrosion. One of the most significant effects of reinforcing steel corrosion on reinforced concrete structures is the decline in the ductility-related properties of the steel. Reinforcement ductility has a decisive effect on the overall ductility of reinforced concrete structures. Different Codes classify the type of steel depending on their ductility defined by the minimum values of several parameters. Using indicators of ductility associating different properties can be advantageous on many occasions. It is considered necessary to define the ductility by means of a single parameter that considers strength values and deformation simultaneously. There are a number of criteria for defining steel ductility by a single parameter. The present experimental study addresses the variation in the ductility of concrete-embedded steel bars when exposed to accelerated corrosion. This paper analyzes the suitability of a new indicator of ductility used in corroded bars.

Outreach Testing of Ancient Astronomy

This work is an outreach approach to an ubiquitous recent problem in secondary-school education: how to face back the decreasing interest in natural sciences shown by students under ‘pressure’ of convenient resources in digital devices/applications. The approach rests on two features. First, empowering of teen-age students to understand regular natural events around, as very few educated people they meet could do. Secondly, an understanding that rests on personal capability to test and verify experimental results from the oldest science, astronomy, with simple instruments as used from antiquity down to the Renaissance (a capability restricted to just solar and lunar motions). Because lengths in astronomy and daily life are so disparate, astronomy basically involved observing and registering values of angles (along with times), measurements being of two types, of angles on the ground and of angles in space, from the ground. First, the gnomon, a simple vertical stick introduced in Babylonia and Egypt, and then in Greece, is used to understand solar motion. The gnomon shadow turns around during any given day, varying in length and thus angle between solar ray and vertical as it turns, going through a minimum (noon time, at a meridian direction) while sweeping some angular range from sunrise to sunset. Further, the shadow minimum length varies through the year, with times when shortest and sun closest to vertical, at summer solstice, and times when longest, at winter solstice six months later. The extreme directions at sunset and sunrise correspond to the solstices, swept angular range greatest at summer, over 180 degrees, and the opposite at winter, with less daytime hours; in between, spring and fall equinoxes occur, marked by collinear shadow directions at sunrise and sunset. The gnomon allows students to determine, in addition to latitude (about 40.4° North at Madrid, say), the inclination of earth equator to plane of its orbit around the sun (ecliptic), this fundamental quantity being given by half the difference between solar distances to vertical at winter and summer solstices, with value about 23.5°. Day and year periods greatly differing by about 2 ½ orders of magnitude, 1 day against 365 days, helps students to correctly visualize and interpret the experimental measurements. Since the gnomon serves to observe at night the moon shadow too, students can also determine the inclination of the lunar orbital plane, as about 5 degrees away from the ecliptic, thus explaining why eclipses are infrequent. Independently, earth taking longer between spring and fall equinoxes than from fall to spring (the solar anomaly), as again verified by the students, was explained in ancient Greek science, which posited orbits universally as circles or their combination, by introducing the eccentric circle, with earth placed some distance away from the orbital centre when considering the relative motion of the sun, which would be closer to the earth in winter. In a sense, this can be seen as hint and approximation of the elliptic orbit proposed by Kepler many centuries later.